The present invention relates to a new and improved displacement detecting arrangement or system in a multi-axis measuring system containing measuring carriages, respectively displaceable along a leading axis and other axes for generating measuring pulses, especially for use with a gear wheel grinding or inspecting or testing machine.
In its more specific aspects, the present invention relates to a new and improved displacement detecting system in such a multi-axis measuring system which includes a primary or main computer for storing predetermined restarting or support points located on the leading axis, a comparator for supplying a measurement triggering or initiating signal to detect the then prevailing respective actual displacement position of a measuring carriage displaced along at least one other axis when one of the restarting points is passed, and a counter whose counted value at the moment when the measurement triggering or initiating signal occurs, is stored in a buffer or intermediate store for.
Displacement detecting arrangements or systems of such kind are used for measuring and positioning purposes in a number of axes, for example, in a gear wheel grinding or testing or inspecting machine. Conventionally one of the axes is selected as a guide or leading axis, which is represented in FIG. 1 as the Y-axis. In case of a particular measuring task, firstly desired reference or set points on the leading axis, so called support or restarting points, are selected or computed. When the measuring carriage to which, in the case of a gear wheel testing or inspecting machine, a sensor is mounted, is advanced along the leading axis, the positions along the other axes are each measured at the moment when the restarting points are passed. Upon passing through the restarting or support points the corresponding values measured along the other axes are determined and also stored. From a comparison of the values associated with the restarting points with the measured values there then result corresponding deviation values, for example, relative to a theoretical involute profile. The measurement time, i.e. the moment of time at which one restarting or support point is crossed, is determined each time by the comparator which initiates measurements along the other axes by means of the measurement triggering or initiating signal.
Incremental scales of high resolution are used in such displacement detecting arrangements or systems, for example, one pulse for one micrometer (.mu.m). When the computer and the counter are organized in a 16-bit format, an amount of data or information can be represented by 2.sup.16 .congruent.64,000 pulses at the maximum. At a resolution of 1 .mu.m this will result in a representable travel path of about 64 mm since otherwise the counter would overflow. If more extended travel paths are processed, there would only remain the possibility of selecting the counter size so large as to correspond to the most extended travel path. This cannot be realized at acceptable costs with travel paths in the order of magnitude of 2 to 3 meters. Additionally, continuously increasing resolutions are presently required, which aggravate the problems in combination with more extended travel paths. Gear wheel grinding and inspecting machines presently are operated, for example, at resolutions in the range of 0.5 to 0.1 .mu.m, so that the representable travel path is still further reduced. Thus, with an increase in the resolution from 1 .mu.m to 0.5 .mu.m only a travel path of 32 mm can be represented with the aforementioned example. For this reason the hardware is required to have a very large bit format, for example 32-bits, by means of which then several meters of travel path can be readily represented, since 2.sup.32 pulses can be processed. A solution of the problem with 32-bit format hardware comprising a counter, a comparator and a buffer or intermediate store (latch) would hardly present any problems with respect to precision and time-delay. However, the expense would become too great in terms of space and circuit components. It would thus be of substantial advantage to find a possibility for effectively using presently conventional microprocessors which usually are organized in an 8-bit or 16-bit format and which could take over part of the task.
It is also conventional practice today to use a computer for calculating positional errors. The computer and the displacement detecting system are placed on different printed-circuit boards or cards which are then interconnected by corresponding buses. This is disadvantageous because additional buses result in specific expenses, for example, with respect to the bus driver, the bus reliability and so forth. It would therefore be particularly advantageous in terms of space requirments and circuitry expense if the entire arrangement for one channel could be based on one printed-circuit board. Due to such autonomous design the processing rate also could be correspondingly increased, because a reduction can be achieved in the amount of data for the common bus and because the synchronization problem would be minimized.
Finally, a further problem results with respect to the recognition of restarting or support point values in such displacement detecting systems in that the occurrence of any time delays must be avoided at any rate at very high resolutions, so that no measuring pulses are lost which otherwise would result in measurement errors. In combination with high operating speeds the high resolution results in input frequencies at the displacement detecting arrangement or system which is in the MHz-range. Up to now, there does not exist any conventional microprocessor capable of handling such high pulse frequencies and operating at a high enough speed which is sufficient to carry out the aforementioned comparison between the restarting point values and the measured values without any errors occurring in that comparison. For this reason, presently a microprocessor computer or microprocessor has only been used as a storing means or store and not as a comparator. This problem, therefore, could only be eliminated by an increase in the operating speed of the microprocessor system or unit.